Mario Santos (on behalf of the Cosmology SWG) Stockholm, August 24, 2015
Why is the expansion of the Universe accelerating? Dark energy? Modified gravity? What is the nature of the primordial Universe? Inflation? Is the primordial spectrum of perturbations non-gaussian? Does the General Theory of Relativity really applies to cosmological scales, or does it needs modification? Is the Universe really isotropic and homogeneous? Is the Universe really flat? Is the Universe really expanding? SKA will not only measure cosmological parameters with more precision, but will answer fundamental questions in cosmology: needs a balance between precision cosmology and discovery cosmology
1. Map the 3D matter distribution on the largest scales and deepest redshifts ever - in order to obtain transformational constraints on primordial non-gaussianity and to perform the first tests of gravity on super-horizon scales. Require a large HI intensity mapping survey 2. Probe the initial conditions and the global features of the Universe through non-gaussianity and the dipole in the matter distribution using high precision measurements of the angular correlation functions. Require a large continuum survey Extra headline science: Map the distribution of HI on cosmological scales from z=20 to z=0 ( make a movie of the Universe! ) SWG first goal: make sure that at least the two top cases are delivered by the SKA and try to achieve other Cosmology cases by taking advantage of other SKA surveys
21 chapters: SKA will be an extremely productive Cosmology machine! (72 Cosmology SWG members) http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=215#session-2107
Current ideas: Distinction between KSPs and telescope surveys KSPs should revolve around major data analysis/calibration efforts, with requirements for large focused teams ( like an experiment using the SKA facility ) More focused scientific products should become work packages within a KSP Great effort should be put on obtaining commensality both in terms of surveys and human resources this will provide huge savings later on 5 Cosmology KSPs are on the table at the moment as a starting point for discussions (for SKA1) -> Ongoing discussions on the wiki: http://skacosmology.pbworks.com
Should produce the largest catalogue of galaxies ever, over the all sky ~ 5x10 8 galaxies, ~ 1 ujy rms (SKA1 should detect ~ 20 times more galaxies than pathfinders with better resolution) Full sky survey ~ 30,000 deg 2 Will need about 10,000 hours ~0.5 arcsec resolution in order to identify FR galaxies See summary in Jarvis et al., arxiv:1501.03825v1
Outputs: Constrain dark energy and modified gravity through correlation with photometric surveys and the CMB (ISW) Tests of isotropy (CMB anomalies?) Test if the cosmological dipole (with radiogalaxies) is the same as the CMB one Constrain primordial non-gaussianity/inflation Planck D. J. Schwarz, et al., PoS(AASKA15), SKA chapters, 2015 SKA1-Mid Ferramacho et. al, MNRAS 2014
The largest weak lensing survey ever done in the radio Highly complementary to optical surveys Crucial to set the path for SKA2 Need ~ 3 (usable) galaxies per arcmin 2 (at least) ~ 5,000 deg 2 ~ 0.5 arcsec resolution (or equivalent uv coverage for shape measurements) KSP or Work package within Cosmology continuum KSP? See: Brown et al., PoS(AASKA14)023
Can probe higher redshifts Synergies with optical to reduce systematics Unique Advantage in radio: polarization and rotation velocity as indicators of intrinsic alignment Not competitive with Euclid expectations but will provide different approach and prepare for SKA2 piggy-back on other survey? Red: 1-sigma/2-sigma constraints for 5,000 deg 2 (~ DES like)
First cosmological survey with HI galaxies (10 7 galaxies!) Great probe for redshift space distortions Given SKA1 sensitivity, focus on redshifts z < 0.8 Optimal survey area ~ 5,000 deg 2 (although 25,000 deg 2 can be acceptable) Propose new band2 definition in order to optimize HI science: 750 1450 MHz SKA 1 Cosmic variance limited SKA 2 See summary in Abdalla et al., PoS(AASKA14)017 See Santos et al., PoS(AASKA14)017 Yahya et al., MNRAS, http://arxiv.org/abs/1412.4700
Not competitive with Euclid. However, correlation with other wavelengths will provide important information Will provide a large catalogue of HI redshifts Will provide a peculiar velocity dataset (for Tully- Fisher) Will prepare for the key project in SKA2 Might be done commensally with other KSP
Technique: use total intensity at each pointing as a function of frequency (no requirement to detect HI galaxies) Need calibrated dish autocorrelations to probe the required scales Crucial for transformational cosmology with SKA1 by-product : the hydrogen content of the Universe on large scales across cosmic time! 3 surveys under discussion: HI Galaxies Maps of intensity See summary in Santos et al., PoS(AASKA14)019
IM survey wish: 0 < z < 3 (1.4 GHz 0.35 GHz), 25,000 deg 2, T sys ~ 20K not possible, so: Survey 1: Large ~ 25,000 deg 2 MID band2 push again to higher z: 750 1450 MHz (0 < z < 0.8) Commensal with continuum? Need on-the-fly scanning strategy (see VLASS) Highly complementary to Euclid Will produce some of the best constraints on dark energy/ modified gravity parameters Error over signal detection level See Bull et al., PoS(AASKA14)024, Raccanelli et al., PoS(AASKA14)031
k = 10-2 Mpc -1 Survey 2: Dish auto-correlations Use MID band1 (current discussions going on - try to match LSST at least) Large survey, ~ 20,000 deg2 Will provide game changing measurements of ultra-large scales best constraints of primordial non-gaussianity and detection of GR effects through cross-correlation with Euclid and LSST using the Multi-tracer technique Survey 3: ~ 1,000 deg 2 survey with SKA-LOW (interferometer) First detections of BAO at z>3 Make sure to close gap with MID HI detections Error over signal SKA1 Euclid See Fonseca et al., http://arxiv.org/abs/1507.04605, Alonso et al., http://arxiv.org/abs/1507.03550
Measure change in z over time of a HI galaxy in order to derive H(z) Mostly a SKA2 KSP but a focused team and initial tests with SKA1 will be important to check the feasibility and experimental requirements Very different calibration requirements from other KSPs
Main surveys and internal commensality between Cosmology KSPs: ~25,000 deg 2 survey in band2 (lowered to ~ 750 MHz) for a continuum survey and a HI intensity mapping survey ~ 5,000 deg 2 survey in band2 for a HI galaxy survey and Weak lensing (issues with spectral resolution requirements ) ~ 20,000 deg 2 survey in band1 (possibly with more sensitivity and bottom frequency at 430 MHz - tbd) for a HI intensity mapping survey and cross-correlations with LSST/Euclid ~ 1,000 deg 2 survey with SKA-LOW to probe the post-reionization Universe on cosmological scales (need SKA-LOW up to ~ 450 MHz) Note: this assumes band2 will be deployed first and that the continuum surveys should be done in band2